PORT HARDY, B.C. - An oily rainbow-like sheen on the waters surrounding a diesel fuel spill off the north coast of Vancouver Island cannot be cleaned up, sparking fears among a nearby First Nation that relies on clam digging for food and economic security.

The thin layer of fuel, which spread more than five kilometres from the salmon farm where the spill originated, has been deemed unrecoverable because it cannot be captured by skimmer vessels or sorbent materials, British Columbia's Environment Ministry said Monday.

Fuel has made contact with some shorelines in the Burdwood Island group, a sensitive area teeming with clam beds that the Kwikwasut'inuxw Haxwa'mis First Nation says are crucial to its economy.

“Would you put that sheen on your vegetable garden?” asked Bob Chamberlin, the nation's elected chief councillor. “They have no technology whatsoever to recover that sheen. That is utterly unacceptable.”

The federal Fisheries Department said First Nations have raised concerns about impacts on shellfish, but most of the area is closed due to biotoxin concerns that existed prior to the spill.

Cermaq Canada, which owns the farm in Echo Bay, about 70 kilometres from Port Hardy, said it “highly regrets” the incident. The leak was discovered early Sunday morning after a staff member mistakenly left a fuel pump on overnight, a spokeswoman said.

Officials now estimate about 600 litres of fuel spilled, less than the 900 to 1,500 litres initially reported. Coast guard crews from Port Hardy were the first to respond and Cermaq has also contracted the Western Canada Marine Response Corp. to help with the cleanup.

Courtney Bransfield, emergency co-ordinator for the Mount Waddington Regional District, said all recoverable diesel was contained to the fish pens by Sunday afternoon. Coast guard flyovers have shown a 5.5-kilometre radius of sheen in waters outside the farm, she said.

“It's unrecoverable material. It's not thick enough,” she said. “It eventually just evaporates.”

However, Peter Ross, an ocean pollution expert with the Vancouver Aquarium, said parts of it will evaporate and other parts will remain droplets in suspension or on the shore.

“The diesel is not going to disappear magically. It's going to continue to weather, get older as a product and end up in different parts of the environment in different forms.”

He said a sheen is a mixture of some diesel components that remain behind after the evaporation of toxic components. Therefore, a sheen is less harmful than other fuel components, but it still shouldn't be taken up by shellfish that are eaten by humans, he said.

Ross, a globally recognized scientist who previously worked for the federal government, said the spill was modest and in sheltered waters.

“If we can't clean that up, then how does that speak to our capacity to deal with large ocean-going tankers with heavy fuel products?” he asked. “I think it underscores the need to improve our ability to respond to these events.”

Cermaq said its salmon are behaving normally after the spill.

Laurie Jensen, director of communications and sustainability, said Cermaq is concerned about impacts to the marine environment and is putting all available resources toward the cleanup. It has also launched a review of procedures to prevent future spills, she said.

Jensen said employees are “devastated.”

“The guys are pretty passionate about what they do and this has hit them pretty hard. They take a lot of pride in their work and to have a mistake made, my heart goes out to them. We all regret that this happened.”